In the fabrication of semiconductor integrated circuits, metal conductor lines are used to interconnect the multiple components in device circuits on a semiconductor wafer. A general process used in the deposition of metal conductor line patterns on semiconductor wafers includes deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal conductor line pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked conductor line pattern; and removing the mask layer typically using reactive plasma and chlorine gas, thereby exposing the top surface of the metal conductor lines. Typically, multiple alternating layers of electrically conductive and insulative materials are sequentially deposited on the wafer substrate, and conductive layers at different levels on the wafer may be electrically connected to each other by etching vias, or openings, in the insulative layers and filling the vias using aluminum, tungsten or other metal to establish electrical connection between the conductive layers.
Semiconductor manufacturing equipment is used to process semiconductor wafers into electronic devices. The equipment includes multiple specialized processing chambers each of which is typically accessible from a central wafer transfer chamber. The wafers are usually loaded into the processing system using a wafer carrier, and into and between the various processing chambers using a transfer mechanism such as a robot. Movement of the wafers throughout the processing system is accomplished using automated handling equipment.
The cost, time and other constraints imposed on the semiconductor fabrication process dictate that the volume, or “footprint space”, of processing equipment be kept at a minimum. Because of this, clearances and tolerances in the processing equipment must be minimized. Proper centering and positioning of semiconductor wafers on a wafer chuck, stage or support is essential for proper wafer processing in order to avoid costly errors such as non-uniform processing and/or wafer breakage. During semiconductor device processing, a wafer must be accurately centered on a wafer support platform or chuck in order to ensure that the wafer will receive uniform processing (such as uniform layer distribution) across its entire face or to ensure that the wafer chuck will not be damaged. Similarly, due to the rapid decrease in mechanical tolerances associated with continually decreasing the footprint space of processing equipment, a wafer must be accurately centered on the transfer mechanism or robot to avoid breakage caused by a wafer falling or striking a wafer component during transport.
Unfortunately, with the limited space and clearances which characterize processing equipment, wafers frequently become misaligned during transport. As a result, the wafer transfer robot may place the wafer in a misaligned position on the wafer support inside the processing chamber. Moreover, over repeated use the wafer transfer robot may gradually drift from parameter specifications and place the wafers in misaligned positions on the wafer support. Semiconductor wafers frequently include a notch or flat area which is engaged by wafer-aligning equipment to facilitate proper wafer alignment or orientation for circuit pattern development and fabrication. These notches are aligned so as to be in the appropriate location with respect to the chamber components for proper processing. As with the wafer transport robot, the notch-engaging wafer-aligning equipment in the chamber may gradually drift from parameter specifications and result in malpositioning of the wafer on the support.
One of the most problematic circumstances in which a substrate is misaligned on a substrate support occurs as the substrate is loaded and positioned by a transfer robot into an ellipsometry tool in order to measure the thickness of an ultra-thin gate oxide layer on the substrate. Malpositioning of the substrate on the substrate support inside the tool results in faulty ellipsometry measurement data for the thickness of the gate oxide layer. Accordingly, a method is needed for determining whether the placement position for substrates on a substrate support strays beyond acceptable deviation ranges for optimum substrate measurement or processing. A method is further needed for expediently re-configuring the substrate position from the misaligned position to the correct position on the substrate support for optimum substrate measurement or processing.
An object of the present invention is to provide a novel method for ensuring proper positioning of substrates on a substrate support.
Another object of the present invention is to provide a novel method for calibrating a homing position for substrate positioning equipment in a processing or measuring tool to facilitate optimum processing or measurement of substrates on a substrate support.
Still another object of the present invention is to provide a novel method for determining whether a position of substrates on a substrate support strays beyond acceptable ranges for optimum substrate measurement or processing.
Yet another object of the present invention is to provide a novel method for preventing inaccurate measurement or processing of substrates.
A still further object of the present invention is to provide a method which includes providing a pair of alignment marks on a control wafer, establishing homing coordinate positions for each of the alignment marks when the substrate is properly positioned on a substrate support for optimum processing or measurement, periodically monitoring test coordinate positions for each of the alignment marks after automated transfer of the substrates onto the support, and determining whether the test coordinate positions deviate from the homing coordinate positions within an acceptable range.
Yet another object of the present invention is to provide a novel method for re-configuring substrates from a misaligned center coordinate position and radial orientation to a homing center coordinate position and radial orientation for optimum substrate measurement or processing.
A still further object of the present invention is to provide a novel method for determining coordinate positions of a center of a misaligned substrate, as well as the degree of shift or misalignment in the radial orientation of the substrate with respect to a homing radial orientation, in order to facilitate expedient re-calibration of the substrate positionining equipment from the misaligned position back to the homing position.